1. Field of the Invention
The present invention relates to systems and devices for stabilizing boats and small ships. More particularly, the present invention relates to gyroscopic stabilizers positioned in boats and configured to counteract rolling motion caused by waves and ship wakes. The gyroscopic stabilizer of the present invention is an active stabilization device.
2. Description of the Prior Art
A rolling boat is uncomfortable and can cause people and animals to experience motion sickness. A device that can create an anti-roll torque can be used to oppose this motion. The difficulty with creating such a device is that a boat is not resting on or in a solid medium that can be used as a base to create an anti-rolling moment. One solution to this problem is to use a large gyroscope to stabilize the boat. A gyroscope is a rotor spinning at a high speed around its spin axis, mounted in a frame that can be moved as the user wishes. When the spinning wheel is turned around an axis (gimbal axis) that is at right angles to its spin axis, a torque is generated around a third axis that is perpendicular to both the spin axis and the turning axis. A gyrostabilizer creates a torque or moment that reduces rolling motion. The gyrostabilizer has a rotor whose spin axis is nominally vertical. The rotor frame is mounted on gimbals so that the rotor can rotate about a transverse, side-to-side axis, but the frame is fastened to the vessel so that the system is constrained to roll from side to side with the boat. With proper selection of the spin and gimbal axes, a torque can be created to oppose roll motion.
Gyroscopic stabilizers (gyrostabilizers) were first used to stabilize very large ships and yachts almost a century ago, and their ability to resist rolling motion (side to side rotation) is well understood. In 1913, the Sperry Gyroscope Company installed a 5-ton gyrostabilizer on the USS Worden, a 700-ton destroyer. Although the device performed as expected, the Navy stopped installing gyrostabilizers at the onset of WW I. Some gyrostabilizers were installed on private yachts in the first part of the 20th century, but other methods of stabilization supplanted gyrostabilizers in the yacht market.
The heart of a gyrostabilizer is a rotor spinning at high speeds. The rotor has three important characteristics:
Weight. The rotor is the heaviest component in the gyrostabilizer machine.
Angular Momentum. The angular (spinning) momentum of the rotor determines its ability to stabilize a yacht or small craft
Kinetic Energy. The kinetic energy stored in the spinning rotor determines how long it takes to start and stop the machine.
The moment of inertia of the rotor depends on both its mass and its mass distribution. The farther mass is located from the spin axis, the higher the moment of inertia that results from the mass. The more the mass of rotor is distributed toward the outer rim of the wheel, the higher the ratio of moment of inertia to its mass.The angular momentum of the rotor is the rotor's moment of inertia multiplied by its angular speed, and a rotor with high angular momentum can create a large anti-rolling torque. To create a lightweight rotor with a high angular momentum, the designer has to rotate it at high speeds.The kinetic energy of a spinning rotor is proportional to its moment of inertia and to the square of its speed. The time required to start or stop the rotor is roughly proportional to its full-speed energy, or to the square of its rotation rate.
When a gyroscope is turned around an axis, called the gimbal axis, which is approximately at right angles to its spin axis, it creates a torque around a third axis, orthogonal to the first two. To create an anti-rolling gyrostabilizer, the spin axis is nominally vertical, and the spinning rotor is tipped forward or backwards on a gimbal axis in the boat. The result is a torque orthogonal to both the spin axis and the gimbal axis. Nominally this torque is aligned with the boat's roll axis, and therefore can be utilized as an anti-rolling torque. The strength of this torque depends on the angle formed by the spin axis and the gimbal axis. Assuming that the boat rotation is primarily around its roll axis, and that rotation around the boat's pitch axis is small enough to be ignored, as the tip angle increases, the included angle decreases and the anti-rolling torque decreases. Accordingly, the maximum anti-rolling restoring torque will be limited to the based on maximum gimbal angles of plus or minus ninety-degrees.
Summarizing the tradeoffs described above:
A high-speed rotor can be lighter than a low-speed rotor.
Low speed rotors can startup and shutdown using less power than high-speed rotors.
The minimum moment of inertia of the rotor is determined by the maximum anti-roll torque required by the boat. This is determined by the size of the boat and the size of the waves or wakes.
Apart from the very large scale passive gyrostabilizer developed by Sperry for Navy vessels of World War I, systems designed to stabilize vessels usually rely upon actuated appendages, such as fins, interceptors or submerged foils, to counteract the rolling effects caused by waves and wakes. Fins, interceptors, and foils all depend on significant forward motion for their anti-roll forces, and are inefficient at low speeds. Prior gyroscope-related anti-rolling systems have either been too massive for relatively smaller vessels, such as yachts, or have been confined to use as a sensing system in combination with a structural element or elements that actually do the stabilizing. There is presently an unfilled need for an effective stabilization system deployable in boats and small ships, especially boats and small ships that are stationary or moving at low speeds.